1. Field of the Invention
The present invention relates to the field of text to speech processing and, more particularly, to training a phonetic decision tree with limited phonetic exceptions for a text-to-speech system.
2. Description of the Related Art
Text-to-speech (TTS) systems are an integral component of speech processing systems. Conventional TTS systems utilize a phonetic decision tree when synthesizing the words contained in an input text string into speech output. These phonetic trees are typically created using a very sizable set of randomly selected words called the training data; the set often contains tens or hundreds of thousands of words. The accuracy of the phonetic tree is then evaluated using test data, which is another set of random words.
Due to phonetic inconsistencies inherent within written languages, these phonetic trees often include extraneous branches to handle such exceptional words. For example, the word “some” is pronounced as “sum” and not with a long ‘o’ as with other phonetically similar words such as “home” and “dome”. When the randomly selected training data contains a large quantity of these phonetically exceptional words, the phonetic tree contains as many extraneous branches. These extraneous branches increase the processing time required by the TTS system to produce the speech output. Additionally, the larger size of the phonetic tree requires more storage space within the system.
Reducing the quantity of phonetic exceptions in the training data would help to streamline the phonetic tree. However, the voluminous size of the training data inhibits the use of a manual process to eliminate phonetic exceptions. An automated process currently does not exist for creating a phonetic tree that is not influenced by phonetic exceptions.
What is needed is an automated solution that creates a phonetic tree without the influence of phonetic exceptions. That is, the solution would use an automated process to remove the influence of phonetic exceptions on the phonetic tree. Ideally, such a solution would result in the creation of a phonetic tree containing only standard phonetic translations. Additionally, this solution can utilize an exception dictionary to phonetize words containing phonetic exceptions.